1. Field of the Invention
The present invention relates to a magnetic recording head used for thermally-assisted magnetic recording in which a magnetic recording medium is irradiated with beam from a plane-emission or surface-emitting type light source, thereby anisotropic magnetic field of the medium is lowered, thus data can be written. Further, the present invention relates to a head gimbal assembly (HGA) provided with the head, and to a magnetic recording apparatus provided with the HGA.
2. Description of the Related Art
As the recording density of a magnetic recording apparatus, as represented by a magnetic disk apparatus, becomes higher, further improvement has been required in the performance of a thin-film magnetic head and a magnetic recording medium. Particularly, in the magnetic recording medium, it is necessary to decrease the size of magnetic micro particles that constitute the magnetic recording layer of the medium, and to reduce irregularity in the boundary of record bit in order to improve the recording density. However, the decrease in size of the magnetic micro particles raises a problem of degradation in thermal stability of the magnetization due to the decrease in volume. As a measure against the thermal stability problem, it may be possible to increase the magnetic anisotropy energy Ku of the magnetic micro particles. However, the increase in energy Ku causes the increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. As a result, the head cannot write data to the magnetic recording medium when the anisotropic magnetic field of the medium exceeds the upper write field limit.
Recently, as a method for solving the problem of thermal stability, so-called a thermally-assisted magnetic recording technique was proposed. In the technique, a magnetic recording medium formed of a magnetic material with a large energy Ku is used so as to stabilize the magnetization, then anisotropic magnetic field of a portion of the medium, where data is to be written, is reduced by heating the portion, just after that, writing is performed by applying write magnetic field to the heated portion.
In this thermally-assisted magnetic recording technique, there has been generally used a method in which a magnetic recording medium is irradiated and thus heated with a light such as near-field light. In this case, it is important to form a very minute beam spot at a desired position on the magnetic recording medium. However, from the beginning, more significant problem to be solved exists in how the beam is to be supplied from a light source to the inside of a head, and specifically, where and how the light source is to be arranged.
As for the supplying of beam, for example, US Patent Publication No. 2008/0002298A1 and Japanese patent publication No. 2005-4901A disclose heads each having a light source arranged on or above an integration surface of a slider substrate. In the head, a surface-emitting laser diode that can be easily mounted on the integration surface is used as the light source and a laser beam from the surface-emitting laser diode is guided to a desired position using a diffraction grating or a hologram lens and a beam-scattering element. Also, U.S. Pat. No. 5,946,281A and Japanese patent publication No. 6-326412A disclose light heads, although not thermally-assisted magnetic recording heads, each of which has a diffraction grating lens for focusing the laser beam from the surface-emitting laser diode.
However, the surface-emitting laser diode used in these documents is a vertical-cavity surface-emitting laser (VCSEL) that is widely used. In a magnetic recording head using such the VCSEL, an insufficient laser output power is likely to lead to serious problems. In a magnetic disk apparatus for performing the thermally-assisted magnetic recording with use of near-field light, the amount of output of near-field light, required for attaining a recording density exceeding 1 Tbits/in2 has been approximately 1 mW with a spot diameter of 40 nm or less, according to the estimation by the present inventors using simulation and the like. Moreover, the beam use efficiency, which the present inventors estimated for the overall optical system in an expected head structure, has been approximately 2%. Therefore, the output power necessary for the laser diode as a light source is estimated to be 50 mW or more. However, a VCSEL generally has a short cavity length, and the output power is about several mW for general use. Therefore, it is difficult for the use of the VCSEL to meet such a high output power.
As aforementioned, according to the conventional technique, it was impossible to use a surface-emitting laser diode having a sufficient output light power and also it was impossible to realize leading of a beam spot with a micro diameter from the surface-emitting laser diode to a desired position.